1. Field of the Invention
The present invention relates to a vibration-proof apparatus for use in a vehicle to reduce transmission of vibration from a vibratory body to a chassis on which the vibratory body is supported.
2. Description of the Prior Art
In general, a vibratory body mounted on a vehicle, such as a differential device or the like, is supported on the chassis through a support member, so that vibration of the vibratory body is transmitted to the chassis via the support member with a specific frequency as a peak value. The thus transmitted vibration having a specific frequency generates another vibration, noisy sound or the like in a cabin of the vehicle, thus resulting in a person occupying the cabin having an unpleasant feeling.
Various kinds of techniques heretofore have been known as measures for preventing the occurrence of such aforesaid vibration. For instance, Japanese Patent Laid-Open document No. 43027/81 discloses a device to reduce vibration generated in a transmission for converting rotation of an engine into driving torque. In that device, a support member for supporting an extension housing of the transmission on a chassis is provided with a tuning mass as a vibratory member adapted to resonate with a vibration having a specific frequency which conducts through the support member. Thus, vibration energy conducted to the support member is intended to be absorbed and damped by consuming it through resonance of the tuning mass so that vibration to be transmitted to the chassis can be reduced.
However, the above device can only deal with vibration having one kind of peak frequency because the tuning mass acting as a vibratory member is fitted directly to the support member. Accordingly, in the case where vibrations having different peak frequencies are transmitted through a single support member, the device can only reduce either one of such vibrations. For instance, in a rear wheel driven vehicle, a differential device as a vibratory body to which the rear end of a propeller or drive shaft is connected is supported on a subframe at the rear part of a chassis of the vehicle. This leads to a result that vibrations having different peak frequencies, comprising vibration from the differential device and vibration caused by imbalance during rotation of the propeller shaft, are transmitted to the chassis. It is difficult for the aforesaid device to effectively deal with reduction of such vibrations.
It is therefore an object of the present invention to provide a vibration-proof apparatus which assures that vibrations having different peak frequencies on a single support member are effectively damped and thereby unpleasant vibration or the like transmitted into a cabin are reduced satisfactorily.